Development of nano-composites following natures example
The development strategy of our partners is based on modifying and optimising the natural and biological designs of nature. It also concerns the optimisation and transfer of nature's knowledge to our technology. In order to be able to technically implement a modified form of these principles, we have to become acquainted with the way in which natural designs and principles function (nano-bionics).
Technical problems can be targeted and resolved easily with minimal materials. The idea is to develop environmentally-friendly, ecologically non-hazardous and comparatively inexpensive binding agent systems and processes that are designed to be sustainable in the long term.
In addition, a new method and process were developed as part of the wood construction material project; we call this the "Nano modification procedure" for wood. This method can be used to manipulate and improve the chemical and physical properties of wood products.
Flammability is significantly reduced and/or prevented completely with this. Inorganic nano-infiltration is used to modify the wood materials completely with inorganic nano-hybrid particles so that the surface of organic wood particles obtains completely new properties. This changes the substance type of the wood materials.
The wood composites are more resistant to environmental interactions. Micro-organisms can no longer grow in these modified wood composites.
These micro-organisms include fungi, yeasts, algae and lichen. They can break down organic materials and contribute to the weathering process over geological periods.
Algae and fungi also cause aesthetic problems on wood materials. Biocides are often used to protect the wood surfaces; they prevent the micro-organisms becoming established for a certain amount of time. After a short time, the micro-organisms (e.g. algae, fungi) start to become established on the surfaces of the wood materials again. Our new wood composites are a perfect solution to this.
Manufacturing procedure for wood composites
The nano-composites made of wood were manufactured using the new "Nano modification procedure" which can be implemented in the near future thanks to our new method. Thanks to another new procedure, the "Nano infiltration procedure", we can improve wood and wood materials and make them more robust.
Plate-type products such as high-density fibreboard (HDF), medium density fibreboard (MDF), chipboard, oriented strand board (OSB), plywood and/or solid wood are particularly suitable to be used as the wood material for the supporting layer. The protective layer that normally consists of at least one external layer (preferably two) is so effective that the supporting layer that would not have been fire-resistant if further measures were not taken is now protected against catching fire.
The structure of the material that has at least two (preferably three or multiple) sheets can be improved by adding or inserting additional layers. For example, adding or inserting veneer layers or plywood layers increases the bending strength of the panel-type material. Decorative layers can be added to at least one external layer.
Inserting ceramics can improve the panel's fire resistance or change the complete characteristics of the panel.
As an alternative or in addition to inserting additional layers, additives can be introduced to individual layers or to all layers to provide the panel-type material with specific properties.
For example, flame retardants, foaming agents (preferably flame-retardant), fungicides and/or insecticides, as well as primers to improve adhesion for decorative cover layers such as wallpaper, can be applied in this way.
The duration of fire resistance (i.e. the time until the material catches fire) depends on the thickness of the outer layer among other things. A high level of fire resistance is achieved with a layer thickness of just a few mm. Increasing the layer thickness improves these properties significantly.
Thanks to the comparatively low layer thickness that is required for fire resistance, the total weight of the panel-type material is only slightly higher than that of a pure wood material panel.
If the edges (i.e. the side surfaces of the panel-type material) are also protected against fire (see fig. 1), this has a particularly positive effect on the fire resistance. This can either be done using appropriate structural processing, e.g by processing edge to edge. However, fire-resistant edge profiles can also be used.
While the panel-type material is being manufactured, the supporting layer of the side edges can also be designed to be fire-resistant, e.g. by impregnating with flame inhibitors or flame retardants. This increases both the fire and water resistance of the panel that was manufactured.
If the wood material is unpressed when it is inserted, the manufacturing process can be carried out without having to take any complex additional measures (see fig. 1, 2, 3), which guarantees that the panels can be manufactured cheaply and practically. If a pressed wood material panel is coated with one or two fire-resistant external layers, this work step can be carried out using known, common presses.
The first external layer is manufactured using a special manufacturing process at first. Then, a single layer or multi-layer wood material panel is applied using a spreading device and finally, a second external layer made of ceramic materials is manufactured. The panel that is manufactured in this way is pressed in advance if necessary and transferred to a press. The panel is manufactured using high temperatures and high pressure for several minutes here.
The press temperature for normal production conditions is at least 130°C to 180°C. The press pressure depends on the wood material selected and the coating. The press duration can also be very different depending on the wood material and the selected procedure.
When manufacturing the wood composites, it is important that the materials can be compressed well when pressing. This jams the particles together mechanically, which also stabilises the external layer. This prevents negative effects on the properties, such as fire resistance for insulation panels in the construction sector, where very low thicknesses are required.
Using light and porous fillers can provide the advantage that air is enclosed in the composite, which improves the insulation properties.
Also equipping the external layer with a seal is no longer required because fire resistance ensures that the wood panels are also water resistant thanks to the ceramics. This is used on outer façades, in the construction sector or for bulkheads in shipbuilding for example.
Compared to common fibreboard panels, the nano-composites as wood panels can also offer the advantage that they have better noise insulation properties because they absorb higher amounts of ambient noise due to the high surface porosity.
The following section provides the facts in detail using several examples:
Wood panel made of softwood shavings with a fire-resistant external layer made of ceramic.
Fig. 1 Softwood shaving is unpressed here and inserted as part of the common manufacturing process. The fire-resistant external layer is made of ceramic.
Air spaces are formed when manufacturing wood composites with a plastic consistency using softwood shavings; this increases the binding volume and therefore improves processability.
The wood material panel can be coated with one or two fire-resistant external layers made of ceramic. This process can be carried out using known systems to spread particle-type materials that are provided with binding agents if necessary, via common presses.
Fig. 2 The softwood shavings were inserted unpressed and processed using the common manufacturing process for wood material panels without having to take any complex additional measures, which guarantees that fibreboard insulating panels can be manufactured cheaply and practically.
An additional silification of the softwood shavings improves mechanical properties and can therefore also increase fire-resistance.
Fig. 3 The softwood shavings were inserted pressed and processed using the uncommon manufacturing process for wood material moulds, which guarantees that different wood moulds can be manufactured cheaply and practically.
The properties of these nano-composites mainly depend on the compression ratio and the materials used. Coarser wood shavings result in increased solidity. The bulk densities of these composites can be varied selectively. For a material density of between 200 and 900 kg/m³, we can achieve pressure resistance values of between 1 and 6 MPa and corresponding bending strengths of between 0.5 and 2.5 MPa.
The analyses of the contraction behaviour indicate that the pressed samples with a higher binding agent ratio have a higher contraction and swelling rate because more water molecules have to escape. Therefore, the contraction rates of the composite that was manufactured achieve values of up to 0.25 mm/m while the relative air humidity is reducing from 70 % to 35 %. The contraction rates of the pressed samples are somewhat higher at 0.5 and 0.80 mm. Here, a higher contraction rate can be observed for the composites with finer wood shavings in comparison to composites with coarser wood shavings.
We were able to find suitable inorganic, nano-structured binding agents to manufacture wood composites without wood pre-treatment. It also turned out that wood composites could also be manufactured using sawdust and other wood residues. The first analyses on the variation of the wood particle shape were carried out. An additional optimisation for the binding agent system that was analysed is possible and promising from a technical and economical point of view.
Nano-modification of wood particles
The wood raw materials were introduced into an inorganic, collodial nano-hybrid sol. The nano-hybrid sols are characterised by a very fine, even distribution spectrum so that they can adhere well to the surface of wood particles by modifying the nano-particles chemically.
Fig. 5 Scanning electrode microscope image (SEM) of bonded sawdust with nano-hybrid sol. The image shows the morphological construction of the surface made of sawdust.
The measurements and the results of the particle size distribution, concentration and the degree of aggregation of nano-hybrid sol is also shown in the following table.
Table 1: The measurement results of nano-hybrid sol
The measurement indicates the particle size distribution, concentration and degree of aggregation for nano-hybrid sol.
In addition to this project, application-related materials in the form of multi-function ceramics with nano-porous to macro-porous structures were developed as innovative solutions for many industrial sectors but which can also be used for other industrial sectors due to the wide range of variation options for the material properties. Therefore, the nano-composites that were manufactured can also be used as substrates for the functional ceramics, weather and fire-resistant or heat insulating lightweight construction materials.
New applications for ceramic materials are in the forefront as technical applications for the following sectors:
• Industrial furnaces and hot gas turbines
• Construction industry, wood industry and high-temperature insulation
• Automotive industry, sound insulation materials
• Environmental engineering and fire protection linings
• Machine, tool and system construction
• Refractories technology and furnace chamber linings
• As binding agents for highly-toxic inorganic connections and radioactive materials
• For high resistance to thermal shock
• Can be used to develop prototypes and moulds
Obviously, the materials that are searched for must also be as non-toxic as possible, widely available and reasonably priced. All of these requirements are important.
Thanks to the development of new materials such as 'ceramic' and new processes such as 'Sol-Gel', amazing advances have been made in the technological area in recent years.
New substances that were created using polymerisation reactions open novel applications and change perspectives that have been regarded as certain in inorganic chemistry for many years.
High temperature techniques are no longer necessary to manufacture materials that have similar structures and properties to ceramics. These substances can condense polymers at temperatures below 100°C, similar to organic polymers.
Our wood doesn't burn!